[alsa-devel] DPCM: BE to BE cpu DAIs question‏

[Liam Girdwood]

On Fri, 2015-06-26 at 10:16 +0800, srv_kaichieh.chaung wrote:
> Hi,
>         Our platform use ASoC structure. Currently, we want to refactor
> our driver to use DPCM structure.
> I followed the documentation of DPCM, but have some trouble
> implementing hostless  BE to BE dai links.
> 
> My question is:
> 1.  Is there any  code example for this(hostless BE to BE)?
> Since I didn't see any existing code on  linux kernel.

I think Vinod has some example code, I dont know if it's upstream yet
but it's part of the Skylake driver. The hostless BE to BE link is
really just a codec <-> codec link defined in the DAPM graph. Iirc,
there are examples of codec <->codec style links upstream in the Samsung
directory.

> 2.  From  documentation,  i have to assgin  a  snd_soc_pcm_stream for BE
> dais.
>      It seems that the BE<->BE dai links can only support one spec
> (format/rates/ch).
>     Or am i getting it wrong, does it support dynamically change of the
> spec?

The BE link can run at any rate/format you need depending on your use
case. It can dynamically change too between use cases. The fixup
callback is used to change the BE config, so it can check any
requirements every time it is called and configure the BE accordingly.
> 
> Thanks in advanced!
> 
> --------------------------------------------------------------------------------------
>   I have  tried some  implementations, but failed.  My linux version is
> 3.18.
> 
> Illustration,
> PCM -----------------> BE1
>                                        ↑
>                                           -------< BE2
> 
> Code snippet,
> 
> static const struct snd_soc_dapm_route machine_routes[] = {
> 	{BE1_PLAYBACK_CPU_DAI_STNAME, NULL, FE_STNAME},
> 	{BE1_PLAYBACK_CPU_DAI_STNAME, NULL, BE2_CAPTURE_CPU_DAI_STNAME},
> };
> 
> static const struct snd_soc_pcm_stream dai_params = {
> 	.formats = SNDRV_PCM_FMTBIT_S32_LE,
> 	.rate_min = 48000,
> 	.rate_max = 48000,
> 	.channels_min = 2,
> 	.channels_max = 2,
> };
> 
> static struct snd_soc_dai_link mt_soc_dai_common[] = {
> 		{
> 			.name = FE_PCM,
> 			.stream_name = FE_STNAME,
> 			.cpu_dai_name = FE_CPUDAINAME,	// cannot use dummy!!!!
> 			.platform_name = FE_PCMNAME,
> 			.codec_name = "snd-soc-dummy",
> 			.codec_dai_name = "snd-soc-dummy-dai",
> 			.init = mt_soc_audio_init3,
> 			.ops = &kc_snd_soc_ops,
> 			.dynamic = 1,
> 			.dpcm_playback = 1,
> 			.trigger = {SND_SOC_DPCM_TRIGGER_POST, SND_SOC_DPCM_TRIGGER_POST},
> 		 },
> 		 /* BE DAIs */
> 		{
> 			.name = "BE2",
> 			.cpu_dai_name = BE2_PLAYBACK_CPU_DAI, //"snd-soc-dummy-dai",
> 			.platform_name = "snd-soc-dummy",
> 			.codec_name = "snd-soc-dummy",
> 			.codec_dai_name = "snd-soc-dummy-dai",
> 			.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF |
> 				SND_SOC_DAIFMT_CBS_CFS,
> 			.no_pcm = 1,
> 			.dpcm_playback = 1,
> 			.dpcm_capture = 1,
> 			.ignore_suspend = 1,
> 			.ignore_pmdown_time = 1,
> 			.params = &dai_params,
> 		},
> 		{
> 			.name = BE1_PLAYBACK,
> 			.cpu_dai_name = BE1_PLAYBACK_CPU_DAI,
> 			.platform_name = "snd-soc-dummy",
> 			.codec_name = "snd-soc-dummy",
> 			.codec_dai_name = "snd-soc-dummy-dai",
> 			.no_pcm = 1,
> 			.dpcm_playback = 1,
> 			.dpcm_capture = 1,
> 			.ignore_suspend = 1,
> 			.ignore_pmdown_time = 1,
> 			.params = &dai_params,
> 		},
> 
> 1. when only  routes  PCM-->BE1,  
>         If i add .params in BE1 soc dai link,  when i start PCM, it will
> crash. and get "Unable to handle kernel NULL pointer dereference at
> virtual address 000000d0"
>         Seems to crash in dpcm_be_dai_startup()

It should not crash. Can you update to the latest kernel and send the
oops message if it still crashes.

>          If i removed .params, it will not crash, and play normally.
> 
> 2.  when only with BE2--> BE1,
>         BE2 is never trigger,  where did i  get wrong?

You need to add the "codec <-> codec" style link here. The code above
only supports 

PCM  <---+---> BE1
         |
         +---> BE2

but BE1/2 cannot initiate the link (they can be seen as slaves) unless
BE1/2 are also linked via codec<->codec style (and are driven by DAPM to
initiate the link).

Liam 
> 
> Thanks.
> 
> 
> 
> 
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